Generator wattage/outlet clarification

[thinkxingu]

Hey All,
Once again, without power and my 5500 watt genny is just barely enough. I'd like to buy a new one, but to clarify: I have a 30 amp Reliance inlet box, 30 amp breaker in my panel (with an interlock), and 10 awg wire. Am I correct in thinking I can run up to 7500 watts through my set-up?

Thanks!

S

 

[Danno77]

Hey All,
Once again, without power and my 5500 watt genny is just barely enough. I'd like to buy a new one, but to clarify: I have a 30 amp Reliance inlet box, 30 amp breaker in my panel (with an interlock), and 10 awg wire. Am I correct in thinking I can run up to 7500 watts through my set-up?

Thanks!

S

I'm not sure I follow. How do you get your 7500 watt total? 5500 is the MAX rating on the genny?

BTW, 30amp x 120v = 3600watts, so thats about the max you can send without tripping the breaker, right? I can't remember this stuff from year to year, lol.

 

[velvetfoot]

I'm totally no expert, but it would be 240 volts x 30 amps, for 7200 watts, right?
I wonder what is happening where you need more juice?
I know I needed one because the 5000 watt unit I had wouldn't run the well pump.

 

[Bad Wolf]

I think he was looking to buy a bigger generator and wanted to see how much it could handle. If you are using a 30 amp breaker for 240 (both sides) then its 30 x240= 7200 watts.
That said I'm running a 7550 watt Troy-bilt with 13500 surge and have never triped out the 30 amp breaker. I have a pump thats listed at 4.8 amp and s.f. 5.9 amp. Not sure what s.f. is, but 4.8 x 240 is 1104. even if start up is 3x thats only 3300 watts. I do know the generator labors briefly when the pump kicks in.
So I don't know if I've ever come close to 7200 watts.

Whats drawing so much?

 

[thinkxingu]

My hot water heater pulls a lot. So it sounds like 120 x 30 x 2 equals 7200 watts max?

S

 

[velvetfoot]

Greg, that sounds like the specs for my Generac, which does start the well pump.

Again, I have no experience, but if there are two elements on the water heater, could one element be disconnected?

 

[thinkxingu]

I was thinking that, but for a little money I could buy a bigger one and not deal with it. My 5500 does most everything, but a bit more would allow me one or two more things, garage opener, one stove burner, etc. We're all electric here.

S

 

[mainemaul]

Hey All,
Once again, without power and my 5500 watt genny is just barely enough. I'd like to buy a new one, but to clarify: I have a 30 amp Reliance inlet box, 30 amp breaker in my panel (with an interlock), and 10 awg wire. Am I correct in thinking I can run up to 7500 watts through my set-up?

Thanks!

Look at the 4 wire 125/250 volt outlet on the generator. If it is a 30 amp you are good.
All you need is a cord and sounds like you should have one already.

S

 

[nate379]

I run my house fine on a 4000 watt gen set.

No I probably couldn't turn every light, TV, and appliance on at once, but why would I need to?

It really depends on what you need the gen set to power. Best bet would be to make a list of everything you would like to power. Then figure out what each draws.

 

[thinkxingu]

As mentioned, hot water alone draws 4k. Add my fridge, and I've trapped out my current genny.

 

[Gary_602z]

A little bit of judicial turning off breakers and you should be able to get by. Once the HW heater is up to temp it should hold it for quite awhile. The fridge can be off for a few hours with no problem, and the garage door should be able to be opened manually.

Gary

 

[thinkxingu]

Right, but if I want to cycle the genny, using it, say, three hours at a time, I need to be able to run the hot water heater and fridge at the save time- especially in the morning. If I do that now, I wouldn't be able to use a burner on the stove, microwave, more than a light or two, etc.

I know I can get by with 5500, I'm doing it now- but if I'm going to replace this one (it's old and was given to me by someone who doesn't take care of his things) it would make more sense and be more efficient if I could buy one that, for the three or four hours I run it in the morning/at night, I could run everything. The alternative would be to run it twice as long (all day) shutting off the fridge or water heater halfway.

S

 

[velvetfoot]

It's never bad to have a spare, either.

 

[wannabegreener]

Right, but if I want to cycle the genny, using it, say, three hours at a time, I need to be able to run the hot water heater and fridge at the save time- especially in the morning. If I do that now, I wouldn't be able to use a burner on the stove, microwave, more than a light or two, etc.

I know I can get by with 5500, I'm doing it now- but if I'm going to replace this one (it's old and was given to me by someone who doesn't take care of his things) it would make more sense and be more efficient if I could buy one that, for the three or four hours I run it in the morning/at night, I could run everything. The alternative would be to run it twice as long (all day) shutting off the fridge or water heater halfway.

S

Im not an electrician, but I play one on hearth.com

I think running any part of a stove will consume lots of power. I probably wouldn't run the stove when the hot water tank is running. If you want to run multiple "big" energy items at once, you should add up the max wattage of each item and look for something a little bigger than that. I have an old 5000 watt generator and my 20 amp 220volt well pump pretty much sucks up all of the power. If I have a light on, it dims when the pump turns on.

Be careful when you are looking for a generator. The number you see is usually max watts, not continuous watts. A 6500 watt generator may only be able to run 4000 continuous. Look for the fine print.

Also in southern nh, but for some reason, we were only out for half a day.

 

[Danno77]

When the power is out, crack out a Coleman camp stove and use it in whatever manner you feel safest. I burn my NG oven and stove without ventilation, so I wouldn't hesitate to boil a quick pot of water on a Coleman stove in my kitchen and then turn it off. If you are leery of the need for ventilation, then cook in the spare bedroom with a window cracked.

As for the water heater, no advice there, except that mine has two elements on it and it takes about 2 minutes to walk down there, use a screwdriver to take the access panel off, then turn the temp wayyyy down on just one of the elements. Don't know if newer water heaters have one control or not, but mine has one for each element. It's not really gonna reduce the total of energy used to heat the water (cause it will take longer to (re)heat the water), but it will reduce the instantaneous usage down to whatever the one element is (1500w or so).

 

[willworkforwood]

hot water alone draws 4k

Do the math before planning to try running everything concurrently with a larger genset. I'm not a pro, but my understanding is that wire ratings are for short-term use (don't know the exact specs), and only around 80% or less of the rated amperage should be continuous. Plus, the capacity is further reduced as the length of the wire increases. So your #10 may be undersized for what you are planning. I have the same setup as you, and have been running a 5550/8550 genset for the past 2 days. It typically runs no more than 1000-1500 continuous watts. But we have a deep well pump that takes around 6600 at startup. My wife now knows not to have the toaster and microwave running when the pump is about to start up (she now also knows where the pump gauge is and how to read it ;-) ). But the pump only runs 2 minutes at 2200, which is no problem in the big picture. You might want to have a pro come in and check to see if you need the gen feed to your house upgraded in order to be able to do what you are planning.

 

[punchy]

Power(watts)=I(amps)xE(voltage)
P=IxE
7200=30x240
10 gauge thhn wire =30 amps

 

[jharkin]

I have that reliance 10 circuit/30amp switch. It will indeed handle up to a 7500 watt generator. (covered in the manual).

With a transfer switch setup you are bringing the input power through a 10/3+G line on a 30 amp twistlock socket. You are getting both phases of 120 so its 30x240 = 7200 (or 30 x 120 x2 = 7200).

So yes you can go up to a 7500watt or so generator.

However if you are trying to run something big like an electric hot water heater Im not sure that will be enough. If you have the reliance wit the fixed breakers they are all 15s and 20s. I don't think 20 is enough for a water heater is it? If its the box that you can put in your own breakers you could put the water heater on a 30 but as you found that could max out even a big gen.


If you REALLY want to power the entire house there is another option. Get a big genset... like say 12KW. Then hardwire in a 50 amp inlet box and line (6/3 +G) to an interlock breaker in your main panel. This would let you run any circuit.

It is critical that if you do this the breaker is an interlock - they have a mechanical device that prevents turning the generator breaker on unless the main breaker is OFF. I have a Siemens panel and I know they make an interlock kit for it - its under $50. I imagine Square D makes one also and there are aftermarket kits.

 

[thinkxingu]

I have an interlock and go direct to my panel with a 30 amp breaker and input box (no transfer switch). I know I can do a jumbo genny, but we've not got natural gas or propane to run it. I've discovered today that I can run the hot water heater and fridge, but the genny trips when (I think) the fridge fires into a defrost cycle. I'm thinking the extra 1700 watts would prevent this.

Another question: is there a difference between a good quality generator's output and a low quality one's? For example, my experience has been that a 100 watt Sony audio receiver is not the same as a 100 watt Denon.

S

 

[mainemaul]

Honda is the King of portable gen sets

 

[muss]

I just bought a Genrac 6500w for $779, free shipping & no sales tax from electric generators online. They have the best prices & biggest selection . All sizes & makes. They are always running specials. Got mine in 4 days. Muss

 

[jharkin]

Big difference in generator power quality. A cheap unit like the 3200 watt generac I have puts out a very rough wave (caused by the vibration and irregular power pulses of the single cylinder engine driving the alternator) that would look very jagged on an oscilloscope. The regulator is a simple governor that tries to keep the engine running at 3600rpm for 60hz output. When you put load on it the engine bogs down and the governor opens the throttle to compensate... the result is that in addition to that rough wave you get some voltage AND frequency drift as the load varies. Some sensitive electronics do not do well on that frequency drift.

As you get into better generators 2 things improve... #1 they use better quality motors that run smoother (honda motors are one of hte best) and #2 they use better quality electronics and voltage regulation and some even filter the power output I think.

The best of the best are inverter generators. Honda makes some of the best as mentioned above. These generate DC and use an inverter to produce AC, putting out a perfect 60Hz sine wave and almost no variation due to load. Ive been told their output is as close to power co quality as a generator can get. They also are much quieter and a bit more fuel efficient because they can idle the engine at low rpm during light load. But the inverter units only go up to 5kw and are $$$$$$

 

[jotul8e2]

We are also an all electric house. That is why we have one of these: http://www.generac.com/Portable/GP/Products/GP_15000E/

I have two transfer switches, one for the house, and one for the shop where my well is located. I run the 50 amp output to the house and the 30 amp out to my shop building, where the well circuit is located. I can run everything: Water heater, oven, microwave, refrigerator, well pump, heat pumps/air conditioners (we have 2, one 4 and one 2 ton), washing machine, dryer, all the lights we want. However, I have not tried to run the furnace heat strip with this; it is on two 30 amp circuits by itself, and I do have a wood burning stove, after all!

It burns about three quarts of gas an hour. I've forgotten the tank size, but I have no complaints.

The generator was cheap compared to the transfer switches.

Consider security in your purchase. Thieves are very active when generators are running. Working in teams they can grab a portable generator and be out of the neighborhood while you are still asking what happened. Stationary units installed on a pad are king here, but a simple chain and padlock can delay them long enough to look elsewhere.

One thing that people tend to forget is that generators need to be used frequently if you are going to count on them. Not only does gas get stale, the brushes and armature in the generator will corrode. I have mine on a calendar to run a couple of hours once every quarter.